ETYM Greek xylon wood.
The woody part of plants: the supporting and water-conducting tissue, consisting primarily of tracheids and vessels.
Woody tissue of plants.
Tissue found in vascular plants, whose main function is to conduct water and dissolved mineral nutrients from the roots to other parts of the plant. Xylem is composed of a number of different types of cell, and may include long, thin, usually dead cells known as tracheids; fibers (schlerenchyma); thin-walled parenchyma cells; and conducting vessels.
In most angiosperms (flowering plants) water is moved through these vessels. Most gymnosperms and pteridophytes lack vessels and depend on tracheids for water conduction.
Non-woody plants contain only primary xylem, derived from the procambium, whereas in trees and shrubs this is replaced for the most part by secondary xylem, formed by secondary growth from the actively dividing vascular cambium. The cell walls of the secondary xylem are thickened by a deposit of lignin, providing mechanical support to the plant; see wood.